The present invention relates to a process for the direct reduction of materials containing iron oxides in a rotary kiln using a solid carbonaceous reducing agent as the fuel and reductant and more particularly, to a method for controlling the sulfur level in the sponge iron or directly reduced iron (DRI) resulting from such a process.
One of the most important restrictions on the chemical content of the DRI product resulting from the direct reduction of ores and other materials containing iron oxides is the level of sulfur in the DRI since severe process difficulties are posed to processors using such DRI for the making of steel by even small amounts of sulfur in their feed stock. Accordingly, a strict upper limit of 0.05% sulfur by weight in the DRI product should be achieved and preferably even lower sulfur levels would be desirable. To this end, a conventional practice in the process for directly reducing iron ores in a rotary kiln using coal fed at both the ore feed and discharge ends, is to add a sulfur control agent, such as limestone or dolomite, to the charge at the feed end of the kiln.
The present invention is directed to monitoring and controlling the key process factors bearing on the sulfur level in the DRI produced by the process to achieve the desired low levels, for example, less than 0.02% by weight, while maintaining process productivity.